Field
The present invention relates a light emitting device and an LCD backlight using the light emitting device. More particularly, the present invention relates to a light emitting device capable of implementing uniform white light and having a wide color reproduction range, and an LCD backlight using the light emitting device.
Discussion of the Background
As high-performance portable information processing devices and mobile communication terminals have been continuously required with the development of information and communication technologies, various kinds of components with high performance and quality have been continuously required in systems. Liquid crystal displays (LCDs), which have been generally applied to monitors of medium- and large-sized terminals such as notebook computers, require white backlight sources at rear side thereof. In a case where a cold cathode fluorescent lamp (CCFL) is generally used as such a backlight source, there are many advantages in that uniform white light with high luminance is implemented, and the like. However, it may be difficult to continuously use the CCFL, because the CCFL cannot be further employed due to the future restriction on the use of mercury. Accordingly, studies on backlight sources with which the CCFLs can be replaced have been actively conducted. Among the backlight sources, a backlight source using a light emitting device has come into the spotlight as a light source capable of substituting for the CCFLs.
A light emitting diode (LED) refers to a device in which minority carriers (electrons or holes) injected by means of a p-n junction structure of a semiconductor are produced, and light is emitted due to recombination of the carriers. Since the LED has low power consumption and long lifespan, can be mounted in a narrow space and has strong resistance against vibration, it has been increasingly employed as components in a variety of information processing and communication devices.
As a prior art of an LCD backlight source using a light emitting diode, an LCD backlight source module has been disclosed in Korean Patent Laid-Open Publication No. 2002-0041480, in which blue light emitted from a blue light emitting diode is converted into white light using a phosphor and the white light is then incident onto a light guide plate for the uniform light distribution, so that an LCD can have uniform light distribution, low power consumption and high durability. In the LCD backlight source module, the blue light emitting diode and phosphor can be used to implement-uniform white light with high luminance. However, since a color reproduction range which can be expressed when light is transmitted into RGB color filters is considerably narrow in a case where the LCD backlight source module is used as a white light source positioned at the rear of an LCD, there is a limitation in the implementation of images closer to natural colors. Particularly, since the above color reproduction range is greatly lower than the color reproduction range provided by the National Television System Committee (NTSC), it is difficult to reproduce more realistic colors.
As another prior art, a method of driving an LCD backlight has been disclosed in Korean Patent Laid-Open Publication No. 2004-0087974, in which a single white light emitting diode or three red, blue and green light emitting diodes are used in an LCD backlight to form a white backlight source, and a microcomputer is used to measure input current and color of each LED and then to adjust the current supplied finally to each LED. A backlight source using three red, blue and green light emitting diodes can satisfy a considerably wide color reproduction range as compared with an existing CCFL, but since thermal or temporal characteristics of the respective LEDs are different from one another, there are disadvantages in that a color tone is changed depending on a use environment, and particularly, the colors are not uniformly mixed due to the occurrence of uneven colors, or the like. Further, there are additional disadvantages in that color coordinates vary due to change in the output of each chip depending on an ambient temperature, it is difficult to implement high luminance and a circuit configuration in which the driving of each LED chip is considered is complicated.